The United States will freeze the assets of seven Ukrainian separatist leaders after discovering new evidence that Moscow is sending tanks and military equipment to pro-Russian insurgents in eastern Ukraine. Washington is also stepping up negotiations with Western allies to impose tougher sanctions on Russia’s military, financial, and technology sectors, a senior U.S. official told reporters on Friday.

The escalation of Moscow’s hand in the simmering political crisis comes as the U.S. turns its attention to Iraq’s civil conflict between Al Qaeda-linked insurgents and the Shiite-led central government in Baghdad. Now Secretary of State John Kerry will have to juggle both geopolitical headaches. On Thursday, President Barack Obama said he is sending Kerry to the Middle East to address the Iraq situation. The senior U.S. official noted that Kerry would also be making calls to allies regarding sanctions against Russia. Reluctance from European countries whose economies are more closely linked to Moscow’s have caused previous efforts to impose multilateral sanctions against broad sectors of Russia’s economy to fail.

"We have been in active conversations with our E.U. partners on what we call ‘scalpel sanctions,’ which would be targeted primarily in financial, defense, and technology sectors," said the U.S. official. "This has been ongoing for some time but has intensified over the last week as we’ve seen Russian materiel move into Ukraine."

On Friday, the Ukrainian government told Western allies that 10 additional tanks, fuel trucks, and other vehicles crossed the border into Ukraine in the last 24 hours. The U.S. official said Washington independently confirmed that additional Russian tanks departed from a deployment site in southwest Russia on Thursday.

The official implored Russia to implement a peace plan aimed at de-escalating the crisis and granting greater autonomy to Ukraine’s restive enclaves proposed by Ukrainian President Petro Poroshenko in recent weeks.

"If [Russia’s] destabilization of Ukraine does not abate and it does not support this peace plan, there will be more costs. More costs in the form of isolation and sanctions," the official said.

The new sanctions target Ukrainian separatist leaders, including: Vyachelsav Ponomaryov, who declared himself mayor of Slavyansk after leading an attack on the mayor’s office in April; Denis Pushilin, leader of the Donetsk People’s Republic, which has ransacked government buildings across eastern Ukraine; and Andrey Purgin, a leader of a council that runs the separatist government in Donetsk. The U.S. will freeze any of their assets its jurisdiction (likely not many).